Static electricity creates problems in the electronics and other industries, particularly with the advent of integrated circuits and other microelectronic components. Components such as integrated circuits, for instance, may be disabled or destroyed by over-voltages or power density resulting from the discharge of static electricity. Certain junctions in such circuits can be destroyed by overvoltages as low as 25 volts, which radically changes the doping structure in their lattices. Power densities resulting from excessive potential and imperfections in circuit layout or structure can vaporize or radically alter the silicon substrate and thus impair or destroy a circuit's performance. Yet a person walking on carpet on a dry day can accumulate as much as 30,000 volts, and he or she can triboelectrically generate thousands of volts by simply changing his or her position in a chair or handling a styrofoam cup.
Such a person can inadvertently discharge such static potential into a circuit or component by touching it and causing over-voltage or excessive power density. Additionally, the potential in such a person's body can induce a charge in a circuit that can later cause over-voltage or excessive power density when the circuit is subsequently grounded.
Those in industries in which integrated circuits and other microelectronic components are handled or assembled may take measures to limit the failure rate of those circuits and components by attempting to keep them as well as their environment at zero electrical potential. Such measures include providing workers and work stations with electrostatic discharge (ESD) devices, such as antistatic carpet, conductive or dissipative grounded desk top work surfaces, hot air ion generators which emit ions to neutralize static changes, grounding wrist straps, heel grounders and other garments to keep workers at zero potential.
The situations in which grounding wrist straps are used heighten the importance of their being effective, reliable, and predictable. The person working on microelectric components or integrated circuits may be completely unaware that he or she has accumulated static electrical charges, and may therefore unknowingly be in a position to disable circuits on which he or she is working or which he or she is handling. If the wrist strap is loose or has been removed or if it is not functioning properly for other reasons, the worker may be unaware that electrical discharges transmitted from his or her fingers are disabling the circuits. (A typical person cannot sense a static electrical discharge of less than approximately 3,500 volts.) No one may discover that the circuits have been disabled or damaged until hours, days or weeks later, when the circuits have been placed in components or devices which fail in the field. Removal and repair or replacement of these circuits once in the field is far costlier than avoiding potential failure while the worker is handling the circuits.
Various procedures for ensuring the proper use and efficacy of ESD devices have been developed. For instance, wrist strap or heel grounder testers have been developed which allow a worker to verify the efficacy of the device. These testing units may be used to continuously monitor the efficacy of the ESD device. Thus, each work station may be equipped with an ESD device monitor which continuously monitors the efficacy of one or more ESD devices and warns the worker in the event of a failure.
Such testing units are of little value, however, if they are not used in a manner which creates confidence that the ESD devices are being tested in a manner that ensures reliable function. Thus, protocols may be established for auditing the monitoring of the ESD devices. For instance, industry standards, such as ISO 9000, may require that manufacturers document any claims that their workers use and verify the efficacy of ESD devices. Thus, where continuous monitoring is used, a record must be made of each occasion on which the failure of an ESD device is detected. These records are then used to certify the products under the applicable standard. Other industry standards or internal operating procedures also may require documentation of ESD auditing programs.
One problem created by conventional methods for recording and tracking of ESD auditing programs is the generation of large amounts of printed documents or records. While such documentation is required, the records can be so bulky and voluminous as to make them practically useless for analytical purposes. Thus, in order to provide the data that can be used in meaningful ways, the records must be entered by hand into a computer database--an expensive and time consuming process. Furthermore, maintaining such records by hand can introduce errors resulting from mis-recording or worker inattention. This is particularly true where continuous monitoring is required, as brief interruptions in ESD device operation may go unnoticed.
Another limitation of manual data entry is the lack of real-time availability of the data to the program supervisor. Currently, if a supervisor wishes to determine whether all ESD devices are operating properly, he or she must go to each testing station and examine the monitoring device and the log book. In a large fabrication facility, the examination of each work station may be difficult or even impossible to do in a short time. Thus, a supervisor has no way of determining which ESD devices are functioning properly at any given time.
In the past, efforts have been made to connect continuous monitoring stations to a central monitoring system. These efforts were unsuccessful, because there was no way to control the flow of data from the continuous monitoring stations to the central monitoring system -- data from multiple stations "collided" on its way to the central system, resulting in garbled, and therefore useless, data. Thus, it would be desirable to provide a system for continuously monitoring the efficacy of ESD devices which allows the monitoring data to be collected and analyzed in a central location in a real-time or virtually real-time manner.